One of the most demanding applications of materials in aircraft gas turbine engines is the compressor and fan disks (sometimes termed “rotors”) upon which the respective compressor blades and fan blades are supported. The disks rotate at many thousands of revolutions per minute, in a moderately elevated-temperature environment, when the gas turbine is operating. They must exhibit the required mechanical properties under these operating conditions.
Certain ones of the gas turbine engine components such as some of the compressor and fan disks are fabricated from titanium alloys. The disks are typically manufactured by furnishing the metallic constituents of the selected titanium alloy, melting the constituents, and casting an ingot of the titanium alloy. The cast ingot is then converted into a billet. The billet is further mechanically worked, typically by forging. The worked billet is thereafter upset forged, and then machined to produce the titanium-alloy component.
Achieving the required mechanical properties at room and elevated temperatures, retaining sufficient environmental resistance, and preventing premature failure offer major challenges in the selection of alloy compositions and the fabrication of the articles. The chemistry and microstructure of the alloy must ensure that the mechanical properties of the article are met over the temperature range of at least up to about 1200° F. for current titanium-alloy components. The potentially deleterious effects of environmental exposure must be avoided. Small mechanical or chemical defects in the final component may cause it to fail prematurely in service, and these defects must be minimized or, if present, be detectable by available inspection techniques and taken into account. Such defects may include, for example, mechanical defects such as cracks and voids, and chemical defects such as hard alpha defects (sometimes termed low-density inclusions) and high-density inclusions. Hard alpha defects, discussed for example in U.S. Pat. Nos. 4,622,079 and 6,019,812, whose disclosures are incorporated by reference, are particularly troublesome in premium-quality alpha-beta and beta titanium alloys used in demanding gas turbine engine applications, as well as other demanding applications such as aircraft structures.
It has been possible, using existing melting, casting, and conversion practice, to prepare titanium-alloy components such as compressor and fan disks that are fully serviceable. However, there is always a desire and need for a manufacturing process to produce the disks and other components with even further-improved properties and greater freedom from defects, thereby improving the operating margins of safety. The present invention fulfills this need for an improved process, and further provides related advantages.